778. A Role of Platelet Apoptosis and Apoptotic Platelet Clearance on Thrombocytopenia in Secondary Dengue Virus infections
Session: Oral Abstract Session: Travel/Tropical Medicine and Parasitology
Friday, October 21, 2011: 2:30 PM
Room: 204AB
Background: Dengue is a serious public health concern in tropical and subtropical countries. Although the earlier studies reported a suppression of megakaryopoiesis in bone marrow of patients with severe disease, the mechanisms of thrombocytopenia have not been fully understood.

Methods: We conducted a prospective hospital-based study at San Lazaro Hospital, Manila, Philippines in 2009 and 2010. Platelet counts, the serum thrombopoetin (TPO) levels, platelet apoptosis and platelet phagocytosis by flowcytometry were examined among 81 patients with secondary dengue virus (DV) infections and 38 healthy volunteers. Apoptosis in cultured human platelets after exposure to DVs was also examined. 

Results: Platelet apoptosis, platelet phagocytosis and the serum TPO levels were significantly increased in these patients during acute and early convalescent phase compared with those of the convalescent phase and healthy controls. While a significant inverse correlation was found between platelet count and platelet apoptosis, a lack of inverse correlation was noted between platelet counts and the serum TPO levels in these patients during acute phase. A significant correlation between platelet apoptosis and platelet phagocytosis was also found during acute and early convalescent phase of these patients. Platelet phagocytosis during acute and early convalescent phase was significantly inhibited by the mutant protein of milk fat globule-endothelial growth factor 8 which is a phosphatidylserine (PS)-recognizing bridge molecule carrying a point mutation in the RGD motif.

Conclusion: An increased serum TPO levels, but lacking a correlation with platelet counts, suggests an involvement of increased platelet phagocytosis, as well as megakaryohypopoesis, as machanisms of thrombocytopenia during acute phase of secondary DV infections. Accelerated engulfment of apoptotic platelets through a PS-recognizing pathway may play an important role on severe or sustained thrombocytopenia in this disease.

Subject Category: T. Travel/tropical medicine and parasitology

Kazunori Oishi, MD, PhD, International Center for Infectious Diseases, Research Institute for Microbial Diseases, Osaka University, Suita, Japan


K. Oishi, None

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